Refrigeration systems are used in many applications for heating and cooling a controlled environment, including a cargo box on a transport truck, train, ship or plane. An important objective of any refrigeration system is to absorb heat by evaporating at low pressure and temperature, and to give up heat by condensing at a higher temperature and pressure. A system's ability to move heat energy in this manner depends primarily on the magnitude of the pressure difference. Consequently, there is a need to establish a large difference in pressure between the high pressure side and the low pressure side of the refrigeration system. To create a large pressure difference it is necessary to establish a high pressure on one side and a low pressure on the other. Unfortunately, the components of a refrigeration system are only designed to withstand certain pressure ratings. If the pressure difference is too great these ratings can be exceeded, then the system components can be damaged. Prior art systems addressed this problem by configuring a control unit to shut a refrigeration system down completely if the system pressures being monitored increased beyond a specified level. As a result, the refrigeration system had to be taken out of service and inspected for problems. Such refrigeration system outages are generally time consuming and costly.